1. Field of the Invention
The present invention relates to a double block and bleed system and, more particularly, to a transmission system for interfacing between an actuating means and a double block and bleed system.
2. Description of the Background
In industries which produce liquid products, particularly beverage industries, such as breweries, soft drink bottlers, dairies, etc., large networks of pipes are used to transfer liquid from one place to another. For a variety of reasons, it is periodically necessary to interrupt liquid flow through a first pipe network while retaining the liquid in a second pipe network normally connected to the first network. Accordingly, valving systems known as double block and bleed are commonly employed.
In a typical double block and bleed system, first and second valves are interconnected by a chamber which is also provided with a bleed valve to drain the chamber, the first and second valves in turn being connectable to respective pipe sections such that the chamber between the valves may be isolated by closure of both of the valves and any material in the chamber may be removed by means of the bleed valve. Additionally, with both of the block valves in the closed position the chamber therebetween can be cleaned with a suitable spray valve in a manner shown as for example in U.S. Pat. No. 4,458,706.
In prior art double block and bleed systems, the block valves are operated by a gear box or transmission assembly which in turn is driven by an actuator which can be manual but which is normally pneumatic or hydraulic. In these prior art systems, both of the block valves are simultaneously opened and closed by the actuator through the transmission assembly. This is disadvantageous because it increases actuator sizing. For example, to open two butterfly valves simultaneously from the fully closed position requires a substantially larger actuator to accommodate the substantially larger initial torque requirements than would be required if the two valves were opened independently.
Moreover, in typical prior art block and bleed systems, the bleed valve requires a separate actuator. The net result is a system requiring multiple and oversized actuators, complex piping and assembly array which is undesirable particularly in piping systems carrying food products where cleanliness is an absolute necessity and bulky, complex systems complicate the problem of achieving cleanliness.